Telephone cable



Feb. 23, 1932. v am-15 1,846,636

TELEPHONE CABLE Filed Oct. 4, 1929 \I v V J 5 7 4 Patented Feb. 23, 1932 UNITED STATES PATENT OFFICE SCHUCKEBTWERKE AKTIENGESELLSCHAF'I, OF BERLIN-SIEMENSSTADT, GERMANY,

A CORPORATION OF GERMANY TELEPHONE CABLE Application filed October 4, 1929, Serial No. 397,224, and in Germany October 5, 1928.

My invention relates to improvements in telephone cables, and more particularly to continuously loaded cables {lirarup cables).

In telephone cables of this type it is of the greatest importance that the properties of the individual conductors should be as similar as possible in order to obtain a cable sufficiently free from cross-talk and similar disturbances. This is very diilicult of attainment in the manufacture of Krarup con ductors because it is impossible to distribute the wrapping of wire, tape or strip quite uniformly over the entire length of the conductor. Apart from this it is necessary that the Krarup conductors should have quite a number of other properties to render them suitable for telephone purposes. The eddy current losses, for instance play an important part. To reduce these losses it has been proposed to divide the loading material into thin layers or laminations, in such a way that a layer of thin ribbon iron is wrapped around the conductor with a considerable overlap, the overlapping layers of iron being firmly pressed together by means of dies or other suitable devices. This kind of Krarup wrapping has like all other transversely wrapped Krarup conductors the disadvantage that the quantity of material per unit' of length varies within wide limits. The rib bon iron is furthermore subjected to considerable tensional stresses during the wrapping around the conductor which stresses have a detrimental eflect upon the magnetic properties of the material.

Another proposal suggests the longitudinal application of ribbon iron to the conductor. This type is, however, not suitable for the construction of cables because the ribbon is too rigidly connected to the conductor and bursts open or forms loops if the conductor is bent or causes sharp bends in the conductor. These bends form a serious danger particularly in cables as they are liable to cause the conductors to break. The longitudinal wrapping has the further drawback that the place of overlap is always located on the same side of the conductor. In this Way disturbances are caused in the cable because the stray fields which are particularly strong at this place are located at one side all along the conductor.

According to my invention these drawbacks are eliminated by wrapping the magnetic material around the conductor in such a way that it forms a helical wrapping of great pitch. Under great pitch is meant a pitchof about 15 times or more thediameter of the conductor. The applied magnetic material may con sist of a single larger or a plurality of layers and be applied on with aright-hand or lefthand twist. This type of wrapping has the advantage that very thin ribbon may be applied to the conductor without subjecting the ribbon to any considerable tensional stresses, and that the quantity of material per unit of length may be kept very constant because the length of the ribbon differs only slightly from the length of the copper conductor to which it is applied. The speed of manufacture of such a Krarup cable is also considerably increased in comparison with the transverse wrapping used or proposed heretofore. The width of the overlap of the tapes or ribbons in my improved cable may be more or less, as desired.

To increase the mechanical strength of the cable a holding member in the form of a ribbon, wire or the like may be placed over the magnetic layer, and may consist of a single ribbon or a plurality of ribbons. This holding member which forces the overlapping portions tightly together in order to keep the air gap or the leakage constant may either consist of an insulating material, or a conducting or a magnetic material. For certain materials the annealing after the wrapping process may be omitted because the material is not stretched or extended but only li htly bent around the conductor. For the ho ding member materials strength may be used or the holding member may be so dimensioned that it possesses great of great mechanical strength to enable it to withstand a very high wrapping speed.

A preferred embodiment of my invention is illustrated in the drawings afiixed to my specification.

In these drawings Fig. 1 shows one way of practicing my in vention, and

Fig. 2, another way, the conductor and the layers applied to it being shown in both figures in elevation.

Referring to Fig. 1 of the drawings 1 is a copper conductor, 2 and 3 represents magnetic ribbon iron wrapped around the conductor 1 at a great pitch. The direction of twist of the two ribbons is in the example I illustrated opposite but it will be understood that the direction may be the same. t is a.

\ holding member which keeps the aforementioned wrapping in position on the conductor.

Magneticmaterials of any suitable kind may be used for wrapping on the Copper conductor. To the wrapping of magnetic material may be applied insulating layers of any suitable kind for insulating the con ductor, as well known in the art. The insulating layers may be so arran ed that they serve at the same time as holding member. Such a design is illustrated in Fig. 2.

Referring to this figure, 5 is a copper conductor, 6 and 7 are the two layers of magnetic ribbon, 8 is a round cord braiding which at the same time takes the place of the holding member. 9 is the usual paper tape wrapping.

Such a cable may preferably be so constructed that the application of the magnetic layers and the holding member as well as the insulation takes place in a single continuous manufacturing operation.

Various changes may be made without departing from the spirit of my invention or the see e of the appended claim.

claim as my invention: a

Telephone cable with continuously loaded 1' conductors, said conductors being helically 40 wrapped with overlapping magnetic tapes, the pitch of said tapes amounting to at least fifteen times the diameter of the conductor.

In testimony whereof I afiix my signature.

ERNST FISCHER. 

